Sorry for going all over the place, but I'll give it a try.
*Keep elites out of SWAT. Well for most playlists for that matter. Bungie always protested there's no difference between the models. If that's the case, why have i never seen an Elite MLG player (oh that sentence is funny)?
*They need to keep the game as Halo Reach and not turn it into DMR Reach. What I mean is don't succumb to the miscreants like what happened to BR 3 and BR 2. So I don't want to see the DMR become the new BR, corrupting every single playlist. Halo 3 was actually quite a bit of fun before all the "mlg" meddling. You actually had to play to the map and weapon layout rather than devolve to "dude, you just got out br'd".
I dropped from level 42 back to 35 with the dramatic change to the game. Which made it impossible to rank back up after so many games of getting used to a single weapon. Grrr.
*Spawn invincibility. Try as they may to avoid it, the spawn trap still exists. It would be nice to be invincible for a few seconds after a spawn to stop the campers.
*Have a "vote to skip" option for the cinemas when doing co-op campaign. It's no fun when people skip these and you want to watch. So something like left for dead.
*Bring back mobile updates. Long ago, msn alerts would send you a text message when your friends popped into halo.
*Record voices during a match. I know, pie in the sky. When you have the watercooler moments though, most of the time you're recreating the conversation that went on during the clip you captured. I don't want to put my PC in the chain so that I can capture everything (ala Halo 1 and 2).
*Kinect. When it worked, aftertouch was fun in heavenly sword. So apply that to head tracking. It is not meant to replace looking with the analog stick, just augmenting it. And use the mic so that I don't have to wear a headset. And track my controller for augmenting grenade tossing or jumping.
*Bring back Pause/FF. On Halo 3, when searching for a clip in the theater, you could hold down FF, then pause. When you unpaused, the game would keep FF'ing. This way you didn't have to hold down the trigger the whole time. Bungie said it was a glitch, and you can't do that in Reach. Noooooooooo.
*Don't mute sound when using active camo. Likewise, tone down the sound of the tired spartan when running.
*Re-release all Halo cinemas, in the box, in HD. What they did with Halo 3 legendary edition in this regard is an abomination.
*Let me use my Reach screenshots as dynamic dasboard wallpaper.
More later. Compile finished.